Back up rifle for North America; What caliber?

Please help me with a decision.

After sitting in my stand last season and noticing my scope had got loose I decided I need to bring an iron sighted "backup" rifle with me in case something like that happens again. I could see banging my scope on something or falling on my rear and "adjusting" my scope. My first thought was a .30-30. Simple, reliable, a decent performer out to 150 yards and ammo is cheap.

I thought then about a backup that I could use for larger North American game. My .30-06 will handle anything on the continent. I'm not so sure about .30-30. I've considered a number of calibers. The ones I really like (.35 Whelen, .444 Marlin, etc...) are either expensive rifles (I'm looking for a backup), ammo is hard to find or both.

I've narrowed it down to .30-30, .35 Remingon and .45-70. I supect the readers or this site are familiar with the ballistics of these calibers so I won't bore you with a description. I'm aware that these are all short range cartridges; that's ok. I'm mostly hunting in thick forest. If you wanted a backup rifle for anything up to and including elk, which of these would you choose?

I'm looking to keep my cost of a rifle low so please no $1000 wonder rifles. When I'm ready I already have my eye on a CZ in .375 H&H.

Help me out please! Thanks.